IMO, ASBA is a reputable company, and they've been offering showcases and camps for many years. The real question to me is, what exactly are you expecting to receive for your $500, and are their better options for achieving those goals? If you just want his numbers documented, the PG showcase covers that. If you're targeting a specific school on the list, a camp at that school may be better. If you're hoping one/any of those schools will fall in love with him, then he's probably very talented and will garner interest from other venues like tournaments or the PG showcase anyway.
Try to read through the current "Exposure -- by time or ability?" thread. The discussion has wandered around some, but it still has some good information in there.